This invention relates generally to aircraft control systems, and, more particularly to a shift mechanism capable of reversibly shifting the control system of an aircraft between a power mode of operation and a manual mode of operation.
A primary source of aircraft control resides in the aileron of an aircraft. The ailerons are the hinged rear portions of an aircraft wing, moved differentially on each side of the aircraft to obtain the lateral or roll control moments thereof. The angular settings of the ailerons are controlled by the operator (pilot) through a flight control system.
The operating principles of the ailerons are the same as for all trailing-edge hinge controlled devices on the aircraft. Deflection of an aileron changes the effective camber, or airfoil curvatuve relative to the wing chord, of the entire wing forward of the aileron. With a trailing-edge deflective upward, reduced local flow velocities are produced on the upper wing surface, and increased local flow velocities are produced on the lower wing surface. By Bernoulli's law, this results in a reduction of lift over the portion of the wing forward of the aileron, and on the aileron itself. Conversely, trailing-edge down deflection of a flap-type aileron increases the lift in the same areas. When the trailing-edge is raised on one wing, the trailing-edge of the aileron on the opposite wing is lowered by a corresponding amount. The decrease in lift on one wing is accompanied by lift increase on the other wing.
As the size of aircrafts continue to increase, the control surfaces such as the wing and associated ailerons have increased in size correspondingly. As a result, devices have been employed to assist the pilot in effecting movement of the aircraft control surfaces. The first type, may be designated as a power mechanism or power unit and may include hydraulic or electrical power devices energized by the movement of the pilot control stick which will therefore exert on the control surface a force much greater than which the pilot is capable himself.
The second type of assisting mechanism is considered a manual control which is in the form of a trim tab connected to the rear portion of the ailerons. Swinging of such a tab in one direction will exert a torque on the main control surface of the aileron tending to swing it in the opposite direction. Since the size of the tab is substantially smaller than the size of the aileron its manual control can be accomplished by operation of the pilot directly from the stick.
Since power units on occasion may fail it becomes essential that the pilot have direct control of the trim tab associated with the aileron. Therefore, a shift mechanism for release or disconnect mechanism must be provided in the aircraft to shift the aircraft from a power mode of operation to a manual mode of operation in a swift and efficient manner. Heretofore, the mechanisms involved for shifting between a power to a manual mode of operation have left much to be desired. For example, in many instances these shift mechanisms have been highly complex and therefore prone to failure, thus becoming, themselves unreliable in operation. In addition, the shift mechanism must operate to shift the control systems between a power mode and a manual mode in a matter of seconds. Any lost time could result in dire consequences to the pilot, personnel aboard and the aircraft itself. Also, many shift mechanisms in use today are irreversible in operation.